MAP (Manifold Absolute Pressure) Sensor
The Manifold Absolute Pressure (MAP) is a sensor that is attached to the intake manifold on a car's engine and responds to changes in the vacuum and provides a reading of it.
5 volts DC is supplied to the sensor from the PCM (powertrain control module). Inside the MAP sensor there is a resistor that moves in relation to intake vacuum. The resistor varies the voltage between about 1V to 4.5V (depending on engine load) and that voltage signal is returned to the PCM to indicate vacuum. This signal is essential for the PCM to determine fuel delivery and is also used some times to determine if the EGR Valve is operating properly.